Monomer vehicles used in die attach paste compositions tend to bleed out onto the substrate during cure, and even (in some cases) during room temperature staging of the adhesive. Indeed, resin bleed is a serious issue for die attach in electronic packaging. "Bleed" is defined herein as separation of the monomer vehicle phase and filler during staging or cure, resulting in spread of resin away from the die bond area. Resin bleed can generate wire bond non-sticks if it flows up onto bonding pads of the microelectronic device itself or the package into which it has been placed.
There are several potential impacts of this problem, e.g., a package assembler must deal with the likelihood of reduced product yields (and the attendant increased costs for manufacture), the part-to-part variability of the bleed phenomenom results in unacceptable part-to-part variability of the desired product, thereby necessitating the additional expense of 100% visual inspection of each component before being passed onto the wire bond step, and the like.
U.S. Pat. No. 4,483,898, issued to Harold Schonborn, et.al., and assigned to AT&T, discloses the use of alcohols, amides, amines, carboxylic acids, and esters containing two to twelve carbon atoms as allegedly being effective for the reduction of spreading of liquid films on substrates. The inhibition of resin bleed for epoxy, acrylate and silicone adhesive systems was the specific focus of this patent. The preferred bleed inhibiting compounds were poly-fluorinated (i.e. where most or all of the hydrogens of the hydrocarbon residue had been replaced by fluorine). The effective range contemplated by this patent is 0.05 to 5% by weight of the liquid phase. It is interesting to note, however, that the bleed control failed at 0.2% by weight of the most preferred bleed inhibiting agent in the absence of any "coupling agent" (see example VII). Furthermore, several of the compounds cited in '898 had deleterious effects on the pot life of the epoxy systems in which they were used (see, for example, Example VIII).
Accordingly, there is still a need in the art for compositions and methods useful for reducing the occurrence of resin bleed when die-attach compositions are applied to a substrate.